When the transmitted signal has?a wide bandwidth gtgt bandwidth of the channel multipath structure is completely resolved by the receiver at any time and the received power varies very little.

When the transmitted signal has a very narrow bandwidth (example the base band signal has a duration greater than the excess delay of the channel) then multipath is not resolved by the received signal and large signal fluctuations occur (fading).

23Example

Assume a discrete channel impulse response is used to model urban radio channels with excess delays as large as 100 ?s and microcellular channels with excess delays not larger than 4 ?s. If the number of multipath bins is fixed at 64 find

(a) ? t

(b) Maximum bandwidth, which the two models can accurately represent.

24Solution

Delays in channel ? t, 2 ? t . N ? t

Maximum excess delay of channel

t N N ? t 100 ? s.

N 64

?t tN /N 100 ?s /64 1.5625 ?s

Maximum bandwidth represented accurately by model 2/ ?t

1.28 MHz

25For microcellular channel

Maximum excess delay of channel

t N N ? t 4 ? s.

N 64

? t t N /N 4 ? s /64 62.5 ns

Maximum bandwidth represented accurately by model 2/ ? t

32 MHz

26Example

Assume a mobile traveling at a velocity of 10m/s receives two multipath components at a carrier frequency of 1000MHz.

The first component is assumed to arrive at t 0 with an initial phase of 0? and a power of 70dBm.

The second component is 3dB weaker than the first one and arrives at t 1? s, also with the initial phase of 0?.

27...Example

If the mobile moves directly in the direction of arrival of the first component and directly away from the direction of arrival of the second component, compute the following

(a) The narrow band and wide band received power over the interval 0-0.5s

(b) The average narrow band received power.

28Narrow band instantaneous power

N-1 j?i (t,t)

r(t)2 ? ai e 2

i 0

Now 70dBm gt 100 pw so a1 v 100 pw

and 73dBm gt 50 pw so a2 v 50 pw

?i 2pd/? 2pvt/?

? (3108)/(100106) 0.3 m

?1 2p10t/0.3 209.4 t rad.

29

?2 -?1 -209.4 t rad.

t 0

r(t)2? v100 ? v50 2 291pw

t 0.1

r(t)2 v100. e j209.4 x 0.1 v50. e -j209.4 x 0.1

78.2pw

t 0.2

r(t)2 v100. e j209.4 x 0.2 v50. e -j209.4 x 0.2

81.5pw

30

t 0.3

r(t)2 291pw

t 0.4

r(t)2 78.2pw

t 0.5

r(t)2 81.5pw

31Wideband instantaneous power

N-1

r(t)2 ? ak2 100 50 150 pW

k 0

32Average narrow band received power

Ea,? PCW 2(291) 2(78.2) 2(81.5) /6

150.233pw

The average narrow band power and wideband power are almost the same over 0.5s.

While the narrow band signal fades over the observation interval, the wideband signal remains constant.

Average period of time for which the received signal is below a specified level R.

57Formula for Average fade duration

? e?2 1

________

?fm?2?

58Example

Find the average fade duration for threshold level ? 0.01, ? 0.1 and ? 1, when the Doppler frequency is 20Hz.

59Solution

? ? e?2 1

?fm?2?

0.01 19.9?s

0.1 200?s

1.0 3.43ms

60Statistical methods for multipath fading channels

Clarks model for Flat Fading

Two-Ray Rayleigh Fading Model

Saleh and Valenzuela Indoor statistical Model

SIRCIM (Simulation of Indoor Radio Channels Impulse Response Models)

SMRCIM (Simulation of Mobile Radio Channel Impulse-Response Models)

About PowerShow.com

PowerShow.com is a leading presentation/slideshow sharing website. Whether your application is business, how-to, education, medicine, school, church, sales, marketing, online training or just for fun, PowerShow.com is a great resource. And, best of all, most of its cool features are free and easy to use.

You can use PowerShow.com to find and download example online PowerPoint ppt presentations on just about any topic you can imagine so you can learn how to improve your own slides and
presentations for free. Or use it to find and download high-quality how-to PowerPoint ppt presentations with illustrated or animated slides that will teach you how to do something new, also for free. Or use it to upload your own PowerPoint slides so you can share them with your teachers, class, students, bosses, employees, customers, potential investors or the world. Or use it to create really cool photo slideshows - with 2D and 3D transitions, animation, and your choice of music - that you can share with your Facebook friends or Google+ circles. That's all free as well!

For a small fee you can get the industry's best online privacy or publicly promote your presentations and slide shows with top rankings. But aside from that it's free. We'll even convert your presentations and slide shows into the universal Flash format with all their original multimedia glory, including animation, 2D and 3D transition effects, embedded music or other audio, or even video embedded in slides. All for free. Most of the presentations and slideshows on PowerShow.com are free to view, many are even free to download. (You can choose whether to allow people to download your original PowerPoint presentations and photo slideshows for a fee or free or not at all.) Check out PowerShow.com today - for FREE. There is truly something for everyone!

presentations for free. Or use it to find and download high-quality how-to PowerPoint ppt presentations with illustrated or animated slides that will teach you how to do something new, also for free. Or use it to upload your own PowerPoint slides so you can share them with your teachers, class, students, bosses, employees, customers, potential investors or the world. Or use it to create really cool photo slideshows - with 2D and 3D transitions, animation, and your choice of music - that you can share with your Facebook friends or Google+ circles. That's all free as well!

For a small fee you can get the industry's best online privacy or publicly promote your presentations and slide shows with top rankings. But aside from that it's free. We'll even convert your presentations and slide shows into the universal Flash format with all their original multimedia glory, including animation, 2D and 3D transition effects, embedded music or other audio, or even video embedded in slides. All for free. Most of the presentations and slideshows on PowerShow.com are free to view, many are even free to download. (You can choose whether to allow people to download your original PowerPoint presentations and photo slideshows for a fee or free or not at all.) Check out PowerShow.com today - for FREE. There is truly something for everyone!